A document filter which restricts input to numeric values, with customisations for decimal precision and negative values

NumericDocumentFilter.java

import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

public class NumericDocumentFilter extends ChainedDocumentFilter {
    
    private int decimalPrecision = 2;
    private boolean allowNegative = false;

    public NumericDocumentFilter(DocumentFilter filter, int decimals, boolean negatives) {
        super(filter);
        decimalPrecision = decimals;
        allowNegative = negatives;
    }

    public NumericDocumentFilter(int decimals, boolean negatives) {
        this(null, decimals, negatives);
    }

    protected boolean accept(FilterBypass fb, int offset, String str) throws BadLocationException {
        boolean accept = true;
        int length = fb.getDocument().getLength();
        String currentText = fb.getDocument().getText(0, length);
        if (str != null) {
            if (!isNumeric(str) && !str.equals(".") && !str.equals("-")) {
                //First, is it a valid character?
                provideErrorFeedback();
                accept = false;
            } else if (str.equals(".") && currentText.contains(".")) {
                //Next, can we place a decimal here?
                provideErrorFeedback();
                accept = false;
            } else if (isNumeric(str) && currentText.indexOf(",") != -1 && offset > currentText.indexOf(",") && length - currentText.indexOf(".") > decimalPrecision && decimalPrecision > 0) {
                //Next, do we get past the decimal precision limit?
                provideErrorFeedback();
                accept = false;
            } else if (str.equals("-") && (offset != 0 || !allowNegative)) {
                //Next, can we put a negative sign?
                provideErrorFeedback();
                accept = false;
            }
        }
        return accept;
    }

    @Override
    public void insertString(FilterBypass fb, int offset, String str, AttributeSet as) throws BadLocationException {
        if (accept(fb, offset, str)) {
            super.insertString(fb, offset, str, as);
        }
    }

    @Override
    public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
        if (accept(fb, offset, text)) {
            super.replace(fb, offset, length, text, attrs);
        }
    }

    public boolean isNumeric(String str) {
        try {
            int x = Integer.parseInt(str);
            System.out.println(x);
            return true;
        } catch (NumberFormatException nFE) {
            System.out.println("Not an Integer");
            return false;
        }
    }
    
}